1. Field
The present disclosure relates generally to aircraft and in particular to refueling aircraft. Still more particularly, the present disclosure relates to a method and apparatus for moving fuel between two aircraft during flight.
2. Background
Air refueling is a process of transferring fuel from one aircraft to another aircraft during flight. A tanker aircraft is the aircraft that typically provides fuel to another aircraft. The aircraft receiving fuel is referred to as a refueling aircraft. This process allows the aircraft receiving fuel to remain in flight for longer periods of time. As a result, an aircraft may extend its range through this type of process. A series of air refuelings may provide a range that is limited only by crew fatigue and maintenance factors, such as engine oil consumption.
Further, when an aircraft can receive extra fuel in the air, the aircraft can takeoff with a greater payload, such as weapons, cargo, or personnel. In this manner, the maximum takeoff weight may be maintained by balancing the larger payload with less fuel.
A tanker aircraft is especially designed for transferring fuel to an aircraft during flight. Various mechanisms may be used to provide the refueling. These mechanisms include, for example, a boom and receptacle system, and a probe and drogue system. With a boom and probe system, a long rigid hollow shaft may be attached to the rear of the tanker aircraft. This attachment is flexible allowing the boom to move with respect to the tanker aircraft. At the end of this tube is a nozzle attached on the flexible ball joint. The nozzle mates to a receptacle that is mounted on the aircraft that is to receive the fuel.
The refueling aircraft flies in formation directly below and behind the boom. When cleared, the aircraft moves forward into a contact position. This positioning may be aided either with voice commands or visual commands from a crew member operating the boom. Once the aircraft receiving the fuel reaches the contact position, the pilot attempts to hold the refueling aircraft in place with little relative motion with respect to the tanker aircraft. When refueling is complete, the pilot of the refueling aircraft may then disengage the receptacle from the boom.
Another system used in refueling is a probe and drogue system. This type of system involves the use of a drogue attached to a flexible hose that extends from the tanker aircraft or boom attached to the tanker aircraft. A drogue is a funnel shaped or cone shaped refueling duct that is towed behind an aircraft. The drogue may function as a target for the probe to create a connection between the tanker aircraft and the aircraft receiving fuel. Further, the drogue itself may include a connector to facilitate the connection between the tanker aircraft and the refueling aircraft.
With a probe and drogue system, the tanker aircraft flies at a straight and level route. The drogue attached to the hose trails behind and below the tanker aircraft. The pilot of the refueling aircraft has a probe attached to the refueling aircraft and flies the aircraft to place the probe directly into the drogue.
This type of system typically requires a closure rate of at least two knots to provide a soft contact to lock valves in the probe and drogue together for refueling. If the speed is too high, damage may occur to the probe or drogue.
If an approach by a pilot of a receiving aircraft to the drogue of a tanker aircraft does not occur at a desired angle and speed, damage to one or more components, such as a probe or valves in the drogue, may occur. Further, if the valves are not properly locked in the drogue and the probe, fuel may spill out.
These types of refueling processes are commonly used for refueling military aircraft. No such fueling has been performed on any regular basis for commercial aircraft. This type of refueling requires training of the pilots flying the aircraft to receive the fuel. As can be seen, from these two currently used systems, pilots flying aircraft receiving the fuel perform a number of different steps for the refueling process, are skilled in flying the aircraft in a manner to engage the drogue or boom, and to maintain a tightly controlled position during the refueling process.